Investigation of UXO from certain types of fin-stabilized mortar training and smoke rounds - Study of reaction when subjected heat

This present report is a continuation of previous work supporting the Swedish Fortification agency with the assessments concerning unexploded ordnances (UXO) remaining on military firing ranges and practice fields after implemented risk reducing measures. The report describe the work done regarding the reaction of heating, from scenarios similar to forest fires, of UXO from certain types of fin-stabilized mortar training and smoke rounds. At the beginning of the work 64 objects, assesed by the Swedish Fortification Agency to be UXO, were inspected by X-ray. The inspection aimed to investigate the actual number of UXO among the objects. From the X-ray it was concluded that 34 of the suspected objects were UXO. The investigated objects originated from different types of fin-stabilized mortar training and smoke rounds: 8 cm rök- och övningsvinggranat m/29-321, 8 cm Rökvinggranat m/502, 8 cm Rökvinggranat m/463 and 47 mm Övningsvinggranat m/404, for which underlying information was subsequently collected. The investigation regarding the type of UXO was also used as foundation for the study of heating on UXO of the same type. Multiple trials were conducted with the aim to study the reaction of UXO subjected to forest fire. The UXO was placed in a fire pit and the reaction and time to reaction was studied. The temperature was measured next to the fuse, next to the body of the UXO and in the fire. The UXO from 8 cm övningsvinggranat m/29-32 reacted after 4 minutes with temperatures in the fire varying between 400-600 °C. ? In two cases, it is estimated that the fuze and the ignition charge have either deflagrated or detonated, resulting in an ejection of fragments. Moreover, smoke generation was noticed for these two grenades. ? In three cases is it estimated that the fuze's blasting cap has initiated without initiation of the ignition charge. The ignition charge is deemed to have been exhausted by either fire or deflagration. Only parts the fuze were broken and ejected. None or a modest amount of smoke was noted. Heating of one UXO from type 8 cm Rökvvinggranat m/50 with homogeneous smoke mass yielded moderate smoke generation. During the trials, air samples and samples of the cooling water were collected. Chemical analysis of the air samples proved to be inconclusive while the analysis of the water indicated occurrence of chloride and hydrogensulfate ion. The obtained results do not contradict what was to be expected if the smoke generating agent consists of sulphur trioxide and chlorosulphonic acid. In order to enable further work regarding risk analysis, generated fragments were collected and thereafter weighed and measured. One trial was recorded such that the velocity of the fragments could be estimated. Numerical simulations were performed in order to complement the conducted trials. The simulations took temperature from the trials as input along with an approximation of a scenario during a forest fire. Depending on the values used for convection and radiation the time until reaction varied between 3,5 and 11 minutes. The numerical results are within a similar timespan as the obtained results from the trials. Additional simulations were conducted to see if a typical forest fire scenario could lead to initiation. With the assumption of a constant surrounding temperature of 800 °C, the time until reaction varied between 1 and 7 minutes. As a result, it cannot be ruled out that unfortunate circumstances might lead to initiation. The obtained results can with some caution be applicable to other 8 cm fin-stabilized rounds.